The allure of hydrogen as a fuel flows from the most basic of chemical formulae: hydrogen plus oxygen equals water. This formula suggests that many of our vehicle related air quality problems could be eliminated simply by fueling conventional internal combustion engines with hydrogen gas.
Unfortunately, this is not the case. Gaseous hydrogen burns faster and hotter than hydrocarbon fuels. Air is 21% oxygen and 79% nitrogen with traces of a variety of other gases and thus hydrogen plus air yields a variety of other end products in addition to water, the most undesireable of which are nitrogen oxides (NOx). In addition, gaseous hydrogen displaces up to a third of the air in the cylinder of an internal combustion engine. This creates an additional complication. If a conventional internal combustion engine is fueled with hydrogen rather than gasoline, the hydrogen burns rapidly which results in unacceptable levels of NOx, and the release of significantly less energy.
A theoretical solution to this problem that is known in the art is fueling the internal combustion engine with water and hydrogen. The addition of water lowers both the rapidity of the combustion as well as its maximum temperature. This makes it possible to increase the power output and simultaneously reduce the high NOx emissions generally associated with hydrogen's fast heat release rate. Realizing this theory has proven difficult.
The specifics of one hydrogen/water fueling system is described in U.S. Pat. No. 3,983,882 to Billings (“the '882 patent). The '882 patent describes the use of a first stage carburetor for mixing H2 and air directly connected to a second stage carburetor that meters water into the H2-air mix. This second stage carburetor is connected to a conventional manifold from which the H2-air-water mix is distributed to the cylinders (the '822 patent, col. 2, lines 16-35). Also described is the use of a first mechanical or electronic fuel injector to inject H2 and a second injector to inject water into the cylinder head (the '822 patent, col. 4, lines 15-21).
U.S. Pat. No. 4,167,919 to Woolley, et al. (“the '919 patent”), describes a carburetor designed to mix hydrogen, gas, and air, and feed the mixture to an engine intake manifold (col. 2, lines 25-19). The '919 patent also describes the use of an injector to inject water into the hydrogen-air stream in place of the carburetor (col. 3, line 66 to col. 4, line 5; and FIG. 3).
Still another hydrogen/water fueling system is described in U.S. Pat. No. 4,508,064 to Watanabe (“the '064 patent”). The '064 patent describes a cylinder 1 having an inlet valve 4 and an exhaust valve 5; a first injector 6, and a second injector 7 port directly into a cylinder (col. 3, lines 25-35). Air flows into the cylinder 1 through the inlet valve which then closes; during the compression stroke the hydrogen gas and water are injected simultaneously or at staggered times and ignited by an ignition plug (col. 3, lines 39-46).
The suggested methods and apparatus of the '882 and the '919 patents solve the back fire and knocking problems that plagued early hydrogen fueled internal combustion engines. However, this can only be achieved by limiting the maximum output to about 60% of the output achieved from a comparably sized gasoline engine. (See, the '064 patent, col. 1, lines 39-59.) The '064 patent indicates that the problems encountered in the '882 and '919 patents are overcome by separately injecting hydrogen gas and liquid water via separate injectors so that the mixing, vaporization of the water, combustion of the hydrogen, etc. all take place in the combustion chamber (col. 2, lines 21-45). 
While the '882, '919, and '064 patents all reduce NOx emissions, none of the metering systems described are accurate enough to reduce NOx emissions to a level that would meet current US standards and simultaneously produce maximum power. (Note, current US NOx emission standards are roughly 1/10 of the current allowable levels in Europe.) Further, all of these prior art systems are too large, require too much space, and cost too much.